/*
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* Copyright (C) 2024 LingYun IoT System Studio
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* Author: Guo Wenxue <guowenxue@gmail.com>
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*
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* A character skeleton driver example in linux kernel.
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*/
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/kernel.h> /* printk() */
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#include <linux/fs.h> /* everything... */
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#include <linux/errno.h> /* error codes */
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#include <linux/types.h> /* size_t */
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#include <linux/cdev.h> /* cdev */
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#include <linux/slab.h> /* kmalloc() */
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#include <linux/version.h> /* kernel version code */
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#include <linux/uaccess.h> /* copy_from/to_user() */
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#include <linux/moduleparam.h>
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/* device name and major number */
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#define DEV_NAME "chrdev"
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int dev_major = 0;
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module_param(dev_major, int, S_IRUGO);
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#define BUF_SIZE 1024
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typedef struct chrdev_s
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{
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struct cdev cdev;
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char *data; /* data buffer */
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uint32_t size; /* data buffer size */
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uint32_t bytes; /* data bytes in the buffer */
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} chrdev_t;
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static struct chrdev_s dev;
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static ssize_t chrdev_read (struct file *file, char __user *buf, size_t count, loff_t *f_pos)
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{
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struct chrdev_s *dev = file->private_data;
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ssize_t nbytes;
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ssize_t rv = 0;
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/* no data in buffer */
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if( !dev->bytes )
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return 0;
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/* copy data to user space */
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nbytes = count>dev->bytes ? dev->bytes : count;
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if( copy_to_user(buf, dev->data, nbytes) )
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{
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rv = -EFAULT;
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goto out;
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}
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/* update return value and data bytes in buffer */
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rv = nbytes;
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dev->bytes -= nbytes;
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out:
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return rv;
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}
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static ssize_t chrdev_write (struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
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{
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struct chrdev_s *dev = file->private_data;
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ssize_t nbytes;
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ssize_t rv = 0;
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/* no space left */
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if( dev->bytes >= dev->size )
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return -ENOSPC;
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/* check copy data bytes */
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if( dev->size - dev->bytes < count)
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nbytes = dev->size - dev->bytes;
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else
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nbytes = count;
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/* copy data from user space */
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if( copy_from_user(&dev->data[dev->bytes], buf, nbytes) )
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{
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rv = -EFAULT;
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goto out;
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}
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/* update return value and data bytes in buffer */
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rv = nbytes;
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dev->bytes += nbytes;
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out:
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return rv;
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}
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static int chrdev_open (struct inode *inode, struct file *file)
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{
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struct chrdev_s *dev; /* device struct address */
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/* get the device struct address by container_of() */
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dev = container_of(inode->i_cdev, struct chrdev_s, cdev);
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/* save the device struct address for other methods */
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file->private_data = dev;
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return 0;
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}
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static int chrdev_close (struct inode *node, struct file *file)
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{
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return 0;
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}
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static struct file_operations chrdev_fops = {
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.owner = THIS_MODULE,
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.open = chrdev_open, /* open() implementation */
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.read = chrdev_read, /* read() implementation */
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.write = chrdev_write, /* write() implementation */
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.release = chrdev_close, /* close() implementation */
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};
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static int __init chrdev_init(void)
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{
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dev_t devno;
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int rv;
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/* malloc and initial device read/write buffer */
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dev.data = kmalloc(BUF_SIZE, GFP_KERNEL);
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if( !dev.data )
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{
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printk(KERN_ERR " %s driver kmalloc() failed\n", DEV_NAME);
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return -ENOMEM;
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}
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dev.size = BUF_SIZE;
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dev.bytes = 0;
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memset(dev.data, 0, dev.size);
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/* allocate device number */
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if(0 != dev_major)
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{
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devno = MKDEV(dev_major, 0);
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rv = register_chrdev_region(devno, 1, DEV_NAME);
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}
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else
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{
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rv = alloc_chrdev_region(&devno, 0, 1, DEV_NAME);
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dev_major = MAJOR(devno);
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}
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if(rv < 0)
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{
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printk(KERN_ERR "%s driver can't use major %d\n", DEV_NAME, dev_major);
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return -ENODEV;
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}
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/* initialize cdev and setup fops */
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cdev_init(&dev.cdev, &chrdev_fops);
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dev.cdev.owner = THIS_MODULE;
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/* register cdev to linux kernel */
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rv = cdev_add(&dev.cdev, devno, 1);
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if( rv )
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{
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rv = -ENODEV;
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printk(KERN_ERR "%s driver regist failed, rv=%d\n", DEV_NAME, rv);
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goto failed1;
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}
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printk(KERN_INFO "%s driver on major[%d] installed.\n", DEV_NAME, dev_major);
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return 0;
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failed1:
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unregister_chrdev_region(devno, 1);
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printk(KERN_ERR "%s driver installed failed.\n", DEV_NAME);
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return rv;
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}
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static void __exit chrdev_exit(void)
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{
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cdev_del(&dev.cdev);
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unregister_chrdev_region(MKDEV(dev_major,0), 1);
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kfree(dev.data);
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printk(KERN_INFO "%s driver removed!\n", DEV_NAME);
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return;
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}
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module_init(chrdev_init);
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module_exit(chrdev_exit);
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MODULE_LICENSE("Dual BSD/GPL");
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MODULE_AUTHOR("GuoWenxue <guowenxue@gmail.com>");
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